Purification techniques, such as chromatography, have been around since the beginning of the 20th century, and are an essential step in downstream operations of industrial processes. Classic chromatography using a single column can be a lengthy and expensive process, due to an inability to perform purification continuously. Simulated Moving Bed (SMB) technology overcomes the intermittent nature of classical chromatography by introducing more columns, thus allowing for simultaneous separation to occur.

There are two aspects of SMB design: the hardware and the process itself. Think of it as a classical music piece. You need the hardware, which is the orchestra. Selecting the musical instruments, how many of each are needed within the orchestra, depends upon the desired symphony – this is the SMB process. Once all the musical instruments are assembled, a musical notation sheet is composed to instruct how and when each instrument is played. The more complex the symphony, the more complex the assembly and the performance.

XPure Systems provides solutions for efficient and customizable construction of a chromatographic symphony. This blog will focus on the assembly of the orchestra via the XPure Design Tool.

Courtesy of Wikimedia Commons.

Basics of SMB Design

As stated earlier, the more complex the process, the more complex the design of said process. Chromatography consists of multiple steps, such as adsorption and elution, also known as zones. Each zone can have multiple positions, which is the place a column may occupy. To advance to the next position or zone, columns must switch. The switch time can be either synchronous, as in the case of carrousel SMB, as evidenced by our XPure-C System. In this setup, all positions are occupied by columns, which experience a continuous flow. At the end of the switch time, all columns are rotated, switching synchronously.

Asynchronous switching allows further optimization of SMB processes. Switch times are defined per position, and, based on the time it takes to cycle through all positions, less columns than the number of positions may be necessary. Complex valve-switching, as present in our XPure-S System, is needed to realize asynchronous operation.

For further details, check out our previous blog about process control for SMB systems. Once all zones are defined in the proper sequence; the process is complete.

Using the symphony analogy, the chromatography zones are, in a sense, the instruments. How many of these instruments are needed? In which order should they be played? And once they are all put together, how long will the symphony last? Will it be as melodious/efficient as desired? The XPure Design Tool enables the user to rapidly design the SMB process by answering all these questions.

Features of XPure Design Tool

At the core of the XPure Design Tool is accessibility and flexibility. The tool can be used to rapidly design SMB processes. The fundamental framework, comprised of linear isotherms and analogies with counter-current heat exchangers, allows easy access design in which a minimum amount of process parameters are needed.

Optimization is based on representative design parameters, and outputs include everything necessary to compare designs and support decision-making. With export of design outputs to the XPure Recipe Manager, design can be transformed rapidly into functional processes with our hardware solutions.

Other features include:

Excel-based accessibility: No special software is needed. The XPure Design Tool is based on Microsoft Excel, allowing maximum accessibility.

Rapid design: The whole design process can be completed in less than half an hour. Every design begins with input of either experimental or literature data, after which a process is constructed. Optimization of the process is based on design parameters, such as number of transfer units, capacity ratio, and adsorption efficiency.

Flexibility: Compatible with various modes of chromatography, such as ynchronous or asynchronous, bind-elute or fractionation, and packed bed or expanded bed.

User interface: Users are guided step-by-step through the design process via an easy-to-use interface (figure 1). Warnings are given if parameters are out of proper design range.

Unit conversion: Conversion of units is integrated into the design tool and allows changing units on the fly.

Process reports: At the end of the design process, a report of the process will be generated, including the most important parameters and a process flow diagram (see figure 2).

Export recipe parameters: After completion of the design process, relevant parameters can be exported for input into the XPure Recipe Manager.

SMB processes are like complex musical symphonies – both require a unique assembly of elements in order to come to fruition. The XPure SMB Design Tool allows for the rapid and accessible construction of the orchestra, thereby streamlining the design process. With XPure Systems solutions, the symphony you have envisioned is just a few steps away. What will you design first, maestro?

Who doesn’t like listening to music? Though music preference varies between people, the basics of creation of music remains the same. Any music, may it be classical, jazz, country, or pop is based on a structured layout of notations, which are played one after the other to create the melody which we like to hear day after day. Do you think if the notations did not exist, the music would remain melodious?

Execution of Simulated Moving Bed (SMB) chromatography processes can be as exciting as playing several musical instruments (the columns) and creating a symphony (the SMB process). Columns in SMB follow a blueprint called recipe to achieve a successful chromatographic process. This emphasizes the importance of errorless, detailed recipes.

The concept of SMB has existed in both the academic and industrial fields for over half a century. Yet, applications have been scarce due to limited knowledge and setups for its implementation. XPure Systems(XPure Systems-Home, 2018) provides a seamless and easy-to-use platform to implement customized SMB processes with its easy to use tools. Barriers in designing the SMB processes are efficiently removed by the XPure Design tool which allows users step-by-step creation of SMB designs based on fundamentals of mass transfer and kinetic equilibrium. This serves for identifying the components or instruments which form the orchestra. To make these instruments work cohesively, either in parallel or in series along the time to create a musical masterpiece, musical notes or punch cards are to be laid. XPure Recipe Manager enables the user to create recipes which form the framework for the execution of the SMB process. The XPure Design Tool details are given in another blog, and this blog is focussed on XPure Recipe Manager.

Basics of Recipe Management

Before going into recipe management of SMB, it is important to understand the operational principles of the technology (Georges Guichon, 1994). For simplicity, let’s consider that in a typical SMB process, several columns switch through different positions executing different functions one after another to maintain the continuity of the process. Each position is given a switch time and process conditions. The conditions define the function and the switch time ensures that the column leaves one position and enters the next position. This can be related to a music piece where violins play the same music piece for the same time after the flutes have finished it or they even play it together if the symphony demands it.

Though the process is well designed and well laid in the minds of the user, capturing and processing all these settings in detail is a cumbersome task. On top of this, the complexity increases directly with the number of columns and that is why a platform which can ensure considering all the minute details through a strategic approach is required. The XPure Recipe Manager provides a two stage approach to solve this issue for both Packed Bed Adsorption (XPure S for PBA) as well as Expanded Bed Adsorption(XPure SMB-EBA) (Pathapati T, 2018). The stages are Recipe Interface and Excel Recipe Manager.

Initially, the Recipe Interface allows the user to define operational zones, which can be common steps in chromatography, such as; equilibration, adsorption, washing, elution, and regeneration. Furthermore, it allows implementation of a position-based methodology to define the sequence of operations through which the columns pass. The first step of the interface lets user to input the project specific and system specific details as obtained from the design tool or lab experiments (screen 1 and screen 2 from Figure 2). In the second step each zone can be further divided by the user into number of positions (screen 3 from figure 2). For each position, data such as column number, column name, flowrates, pump configuration, switch times, sampling, and sensor-based switching conditions, can be filled or selected in the interface.

Additional advantage of XPure recipe manager is to gain control on a niche technology of Expanded Bed Adsorption (EBA) SMB. Using features of % active level bed control and expansion factor, it is possible to layout a recipe for a better control of EBA.

Once all steps of in the Recipe Interface are completed, the process data from interface is transferred to Excel Recipe Manager for further processing and validation. Both Recipe interface and Excel Recipe Manager are implemented in excel making them very easy to access, use, and edit when required. The following checks are and options are available in the Excel Recipe Manager:

Redundancy check: The process settings are searched for errors throughout the sheet. Duplicates, errors, and important fields are highlighted to capture the user’s attention and decrease the number of errors in the final recipe.

Time simulation: Simulation is carried out to check how columns travel through different positions throughout the recipe. It provides a visual aid for the user to foresee that the execution is without errors.

Sampling: Users can create a sampling matrix and define the number of samples to be taken based on time or sensor data.

Export: Once checked and validated, the Excel Recipe Manager enables the user to export all the process settings into a text file to be imported into the XPure Automation Software for direct execution of the recipe.

Detailed stepwise execution of the XPure Recipe Manager is provided in the user manual for easy understanding and implementation.

Conclusion

For both symphonies and SMB processes, it is of utmost importance to have a strategic framework to define when, what should be executed, be it a musical note or a column switching. The XPure Recipe Manager provides an accessible platform to create recipes for XPure SMB Systems through its user interface and excel based ‘push button’ approach. It allows efficient translation of design data into errorless recipes, while streamlining process implementation into the XPure Automation Software. A strategic methodology of SMB implementation through recipe management creates a fundamental understanding in the users, aiding into educating them in this specific technology implementation.

The portfolio of plant-based products in the supermarkets is expanding. In 2018, a study indicated that the plant-based food market is growing at a 10 -old higher rate compared to overall food market growth (Schroeder, 2019). Market share of plant-based products like meat alternatives, vegan foods (milk, cheese, and yoghurt) and nutraceutical compounds has seen steep increase.

Over the centuries, both plant-based and animal-based diets for humans have gone through an evolution to feed the growing population and meet nutritional requirements. The evolution in agriculture resulted in higher productivity and a reduced environmental footprint through the adaptation of modern and smart agricultural practices. On the other hand, evolution of cattle and poultry farming resulted in higher output at the cost of increased nitrogen and methane gas emissions, inefficient utilization of natural resources like water, and protein-rich feedstock from agriculture (cattle feed). Therefore, plant-based foods are still considered to be more sustainable.

The overall sustainability of the agricultural industry depends on the processes involved in converting the harvest to marketable food products. Therefore, it is critical to employ efficient processes to handle plant-based input streams, where complementary choice of feedstock and process technologies defines techno-economic feasibility. In this blog, we provide an overview about how traditional versu highly-selective separation techniques in plant protein purification can influence the outcome with respect to selectivity, operability, scalability, OPEX, and CAPEX. Evaluation basis is:

Selectivity: Degree of freedom to optimize the operating window for high separation efficiency.

Operability: Number of critical process parameters to be monitored and controlled.

Scalability: Number of scale-limiting factors.

OPEX: Raw material, utilities, and energy consumption.

CAPEX: Capital investment and technology lifetime.

Traditional Separation Technologies:

Process Technology

Selectivity

Operability

Scalability

OPEX

CAPEX

Extraction

Good

Average

Good

High

Medium-high

Precipitation

Good

Good

Good

Medium

Medium

Solid-liquid separation

Average

Good

Very good

Medium

Medium

Neutralization

Poor

Very good

Very good

Low

Low

Drying

Poor

Very good

Good

High

High

In the case of the above-mentioned traditional technologies for plant protein purification, selectivity is one of the major concerns because these technologies employ only one separation principle. Even though extraction and precipitation exhibit better selectivity due to the higher degree of freedom to use optimum solvents and precipitating agents, they are often not sufficient enough to handle complex plant-based feed streams with a number of off-flavor compounds and other impurities. Therefore, in this scenario, often the process selectivity becomes a bottleneck to achieve desired product quality.

Separation Technologies with High Selectivity:

Process Technology

Selectivity

Operability

Scalability

OPEX

CAPEX

Adsorption/ Chromatography

Excellent

Good

Excellent

Medium-high

Medium-high

Crystallization

Very Good

Very Good

Good

Medium-high

Medium-high

Hybrid Technologies

Excellent

Good

Average-good

Medium-high

Medium-high

Separation techniques like crystallization, adsorption/chromatography are traditionally known for improved selectivity and hybrid technologies like adsorption-membranes, pervaporation, centrifugal extraction etc. are also used to efficiently address complex separation challenges. Among these technologies, crystallization is an easy technique to operate, while chromatography and hybrid technologies are excellent with respect to selectivity. However, proteins can be sensitive to aggressive process conditions (very high temperatures, etc.) in the case of hybrid technologies and crystallization can be energy-intensive at very large scales. Among the three options, adsorption/chromatography in batch or SMB mode is one of the few techniques operated under close to atmospheric conditions and ideal for both selective removal of off-flavors and protein capture. However, in order to enable its application, robustness and operational efficiency must be improved by reducing buffer consumptions and resin utilization through approaches like continuous processing. This will promote the SMB mode of chromatography operation as a possible solution to enable sustainable processing of plant-based feedstock.

XPure Systems was invited to join the Industrial Advisory Board (IAB) of SepCon (Seperations Consortium). SepCon works to move cost-effective, high-performing separations technologies to the market faster through coordinated research at the national laboratories that target challenges relevant to industry and the U.S. Department of Energy, Bioenergy Technologies Office (BETO) pathways.

SepCon interacts with an external Advisory Board consisting of industry, government, and academic representatives who help the Consortium maintain an industry-relevant focus and knowledge of recent technology advances and challenges. This Advisory Board (IAB) meets with the Steering Committee and team leads to address topics including biomass fractionation, recovery of dilute carbon from aqueous streams, purification, process improvements, and catalyst preservation.

Last month, René Nanninga and Trinath Pathapati from the XPure team attended the #AIChE Annual Meeting in Orlando (USA). The AIChE (The American Institute of Chemical Engineers) Annual Meeting is the premier educational forum for chemical engineers interested in innovation and professional growth. Academic and industry experts covered a wide range of topics relevant to cutting-edge research, new technologies, and emerging growth areas in chemical engineering. More than 7,000 delegates (professors, scholars, scientists, engineers and graduate students) from across the globe attended the event. At our booth, we exhibited our XPure S simulated moving bed (SMB) and XPure E expanded bed adsorption (EBA) systems. We also presented continuous ion exchange and chromatographic separations to the visitors. More than 50 technology-specific interactions took place between the XPure team and the delegates.

XPure Workshops at #AIChEAnnual Meeting

Trinath hosted two workshops during the event. On Tuesday, November 12, he spoke on how to achieve purity, productivity, and profitability demands of process industry using simulated moving bed technology. This topic was focused around complex biological streams in process industries, which require efficient downstream technologies. SMB chromatography is known to be a potential alternative to efficiently process multi-component streams. The focus was to understand the state-of-the-art XPure SMB technology. This technology was assessed based on key industrial drivers like flexibility, operability, and scalability. Finally, we presented several tested and proven case studies. These cases described the impact of XPure SMB technology on purity, productivity, and profitability outcomes in specific industrial settings.

Trinath also presented another workshop about how to design, build and implement integrated technologies like EBA in SMB mode. During the workshop, Trinath discussed the role of EBA technology as a smart separation step for bio-based streams and its impact on product purity, productivity, and yield. This workshop highlighted the benefits of performing EBA in SMB mode and the approach to design, build, and implement EBA-SMB. Finally, Trinath reviewed a tested and proven case study to describe the approach of implementing EBA-SMB and the resulting impact on process efficiency and economics.

Techno-economic evaluation (TEE) is an approach that helps holistic decision-making during development and optimization of manufacturing processes in food, pharma, chemical and bio-based industries. In this article, we will present three major overviews, which can help in structuring the development path for translating optimal technological outcomes into economically viable industrial processes. The three overviews presented below include:

Feedstock and Product overview

Process overview

Economic overview

Each of these overviews present some fundamental blocks that allow to analyze the requirements and enable the technological outcomes to address the demands.

Feedstock and Product Overview

The primary overview for conceptualizing a feasible process is a feedstock and product overview. Such an overview presents the basic elements to be understood when deriving a product(s) from feedstock. The overview can involve five generic blocks, which include the type of industry, feedstock used by the particular industry, physical properties of the feedstock, required production process and the final product. In Figure 1 below, an example is presented for the food industry, where the feedstock can be either plant-based or animal-based, where the plant-based feedstock then can involve both solid and liquid streams. Therefore, a process required must enable purification of liquid streams or extraction of valuable components from the solid stream into a liquid stream and further purification. A purification/separation process with suitable technologies will therefore define the product quality and resulting value. Like mentioned in Figure 1, a purification process can result in plant-based nutraceuticals, sugars, proteins etc. of different market values and economic potential.

Figure 1: Feedstock and product overview

Process Overview

The feedstock and product overview presents the process targets depending on the specifications of feedstock and the product‘s market requirements. Based on the defined process targets, the process overview can be generated with five generic blocks as described in Figure 2 below. The primary block involves understanding a generic or existing process for manufacturing a specific product from a feedstock. Then, critical factors to be addressed by such a process when optimized are defined in a critical factors block. This is followed by identifying critical process steps, which can have a major impact on the critical factors. The critical factors can always depend on one or more critical process steps. In Figure 2, when the critical step is chromatography, the mode of operation and type of columns used will affect the resulting critical factors. Therefore, a preliminary process development plan needs to be generated to obtain an optimal operating window for the chromatography step to achieve the critical factors.

The process development outcome is then incorporated into an economic overview described in Figure 3. Economic overview can then be used to understand the critical cost contributors and further optimize the process to achieve the desired process economics. As an outcome of the product, process, and economic overviews, a techno-economic optimization strategy can be derived according to Figure 4, further leading to a techno-economically viable manufacturing process.

In fermentation-based processes, products are produced in diluted environments to prevent microbial growth inhibition by the products or the by-products. Consequently, downstream processing (DSP) is usually composed of several unit operations, which translate into higher costs for the overall process (e.g. for biopharmaceuticals DSP costs can represent 80 % of the total costs) and reduced overall yields. Therefore, there is a need to use process technologies that can improve process economics.

IN SITU PRODUCT REMOVAL

As bioprocessing is moving towards continuous modes of operation, in situ product removal (ISPR) is an interesting strategy to improve the DSP efficiency. ISPR enables the product separation during fermentation. However, ISPR requires unit operations that can perform primary product recovery.

PRIMARY RECOVERY STRATEGIES

Traditionally, centrifugation and membrane technologies are preferred for the primary recovery. Nevertheless, fermentation streams are sensitive to mechanical forces and complex to process smoothly using membrane operations. Consequently, with this strategy, there will be considerable amounts of product that degrades and cells that die before the broth is recirculated back into the fermenter. Therefore, a membrane filtration is not a viable option. Could chromatography be used instead then? The answer is yes.

Fermentation streams cannot be processed using packed bed chromatography, but they can be effectively processed using expanded bed adsorption (EBA) chromatography!

EXPANDED BED ADSORPTION (EBA)

EBA is a chromatography technology that combines cell removal, product capture and initial purification step in a single-unit operation. As a typical adsorption process, the adsorbent is kept inside the column where the product stream flows through. In EBA, the liquid stream flows upwards, enabling the adsorbent resin beads in the column to become fluidized (expanded). Thus, the particulate biomass can flow through the bed void [1].

IN SITU PRODUCT REMOVAL WITH EBA

The fermentation broth is directly fed into the EBA column, and, due to the selective interaction between the target compounds in the broth and the resin beads, a selective separation is achieved by capturing product and allowing the cells to flow through. The adsorbed product is collected later on, in an elution step.

This process does not result in any cell disruption. New media can be added to the flow through stream and recirculated back into the fermenter to improve the productivity using cell recycling.

FINAL REMARKS

Could this strategy be applied in your process? Then take a look at how XPure-E system could simplify the performance of EBA and contact us for more information. Let us discuss feasibility for your product.

ECCE12/ECAB5 this year has been successfully held in Florence, the city of renaissance. The event was attended by more than 1,000 delegates (Professors, Scholars, Scientists and Graduate students) from across the globe. The event strongly resonated the fundamental objective to share state of the art developments in the field of chemical engineering and applied biotechnology. The keynote was vocal that it is the time for:

”Renaissance in Chemical Engineering”

Plenary Lectures: Some of the Pioneers in Chemical Engineering shared insights about some important elements that can help in achieving a Sustainable Chemical Industry. The lectures included some fundamental aspects like the need for a change in Chemical Engineering education and the use of Chemical Markup Language in writing, which can enable efficient use of reliable literature. Some other major topics included Process Intensification, Process Safety and Waste Recycling.

Process intensification has been addressed from both feedstock to product conversion and product purification aspects. Product conversion highlights mainly involved CO2 utilization and several chemical, catalytic and bioprocess alternatives were presented to convert CO2 to building blocks includingindustrial realization of Syngas Fermentation. An interesting approach was also presented as 5G biorefinery to use electricity and CO2 to produce building blocks. Purification highlights included recent developments in extraction, membrane separation and adsorption/chromatography technologies.

As XPure Team we are glad to have been part of ECCE12/ECAB5 as bronze sponsor. About 100 delegates participated in our talk on EBA-SMB Technology with very constructive questions after the talk. We were also able to exchange some interesting ideas to collaborate and become part of building Sustainable Chemical Industry.

Several organic and amino acids have found applications as specialty molecules in food, consumer goods and pharmaceutical industries. Itaconic Acid (IA) is a 5 carbon dicarboxylic acid produced through bacterial fermentation and used as an important building block for biopolymers. In case of IA production, downstream processing can account to 30-50 % of the overall cost of goods (COGs). Therefore, it requires effective and efficient operations to improve sustainability and cost competitiveness. In the current article, we will briefly discuss the role of expanded bed adsorption (EBA) and simulated moving bed (SMB) technologies in production of IA.

The basis for selecting a specific unit-operation is defined by desired separation. Typical fermentation output stream contains 5-10 % IA, 5-10 % impurities and 80-90 % water. Impurities include both suspended solids like biomass and dissolved compounds that are produced as co-metabolites. Though precipitation is an easy method for IA purification, it results in formation of by-products and limits product purity. Therefore, instead of precipitation, adsorption using a chromatography resin is a preferred alternative. However, feed for packed bed chromatography columns need to be free of suspended solids and this require additional unit operations for clarification, resulting in yield losses and higher costs. To overcome these limitations, Expanded Bed Adsorption (EBA) can be applied. EBA is an integrated adsorption process, where the product is selectively captured by fluidized adsorbent beads from unclarified fermentation broth. Thereby, enabling removal of both suspended and soluble impurities in 1 step.

Successful EBA process can achieve desired product purity with high recovery yields using 30-60 % less number of unit-operations. In addition, it is easier to scale EBA for large-scale production processes with several kilotons annual capacity, due to no pressure drop limitations. However, it is important to note that application of EBA on large scale can lead to large side streams, which require processing before recycling or release into the environment. Additionally, fluid distribution and hydrodynamic performance of EBA may result in reduced dynamic binding capacity compared to packed bed. A prudent approach to overcome these limitations is by operating EBA in SMB mode.

In conclusion, EBA in combination with SMB mode enables continuous operation, reduced number of downstream steps, improved resin + buffer utilization and enhanced productivity, which makes it a techno-economically viable technology for IA production process. For more information on the EBA and SMB technologies please have a look at www.xpure-systems.com or you can contact us via Dit e-mailadres wordt beveiligd tegen spambots. JavaScript dient ingeschakeld te zijn om het te bekijken..

This blog focusses on useful and valuable proteins in both milk and whey that can be recovered with chromatographic separation.

Milk and its derivatives contain various proteins that are useful as human nutrition. Milk proteins are especially rich in amino acids that stimulate muscle synthesis. In addition, some proteins and peptides in milk have positive health effect e.g. on blood pressure, inflammation, oxidation and tissue development [1]. Some people suffer from deficiency of specific proteins, In order to to find a solution for this, manufacturers produce balanced, composed (semi-)synthetic milk products, e.g. baby food, by adding those proteins in the manufacturing process.

This blog describes a few examples where adsorption chromatography can serve as a separation technology to isolate useful milk and whey proteins.

Minor Milk Proteins

Above Figure 1 represents the average milk protein composition in both human and bovine milk (note that only the “high-value” minor proteins are represented in this figure, because the majority (i.e. > 80%) of cow milk proteins consists of different types of casein. For human milk approximately 40% of total protein consists of casein).

Total bovine milk proteins content amounts to 30-34 g/l.

PROTEIN ADSORPTION

In expanded bed mode, suited to direct the fermentation broth to the adsorption process, without having to clarify the crude broth first, it has been found that the feed flow rate can be substantially higher (~10 m/h or even higher) without significant backpressure [6].

Before loading milk on a chromatography column the fat (components) need to be skimmed first in order to prevent blockage of the adsorption phase, and reduce viscosity to attain higher bed flow rates.

Dairy Characteristics

Milk is a complex medium; in addition the composition of milk is subject to seasonal influences. and further pooling prior to processing is quite common in dairy industry. Volumes to be processed lie in the range up to 100’s of m3’s per day.

Since the proteins are utilised in food supplements, regulatory and hygiene rules apply.

Pasteurisation is a common step in milk processing, temperature largely affects the adsorption characteristics and may also pose additional demands on the adsorption materials in terms of thermosensitivity.

Adsorption Technology

Figure 2. Part of flow scheme to recover milk proteins, including chromatographic adsorption

Figure 2 conveys part of a typical milk process where fat and protein are separated.

The Adsorption step comprises the capture of specific proteins to a specific, selective resin, and the elution with a proper salt buffer.

Depending on the magnitude of the process, as well as process control requirements, the adsorption step may be operated in a continuous mode. A well established continuous chromatography mode is based on simulated moving bed technology (SMB). This technology features a multiple (typically 4-16) column process that smartly accommodates all distinct process steps –running simultaneously- that are part of the bind and elute process, including wash/rinse/equilibration and regeneration.

XPure has developed a SMB system that can be operated both in fixed and expanded bed mode, so called Expanded Bed Adsorption (EBA). This EBA mode features all individual steps of the SMB process cycle, operated in upflow / expanded bed mode, refer to Figure 3.

Note: Regeneration has not been included, every column can be read as a zone consisting multiple columns,, either in series or parallel

Process cycle time and specific residence time in certain zones may be adapted to changing input parameters, e.g. protein content and composition.

Case studies have been done both for lacto-peroxidase and lactoferrin. Based on packed bed mode for a daily milk production of 70 m3 a continuos process for lactoferrin would result in significant cost reduction in cost of goods, refer to Figure 4. A significant part of the cost reduction in SMB-mode in relation to batch-mode chromatography, can be related t0 consumables. It has further been found that skimming is necessary to reduce the residual fat content below 0.1 w-%, prior to applicable chromatography processes.

XPure EBA-SMB has been successfully run on amino-acid containing fermentation broth without prior clarification or filtration. This process design can directly be translated to the milk protein application and could flexibly be fit in any process step that the skimmed milk goes through.

Conclusion

For large-scale dairy processes cost reduction can be attained by a continuous operating mode. For the adsorption process, simulated moving bed chromatography (SMB) is a state-of-the-art technology that contributes to a high level of process automation, product quality and yield.

The XPure SMB-EBA offers the additional feature to process the unclarified (skimmed) milk directly, and so reducing operational and capital costs. For further information you are invited to contact us at Dit e-mailadres wordt beveiligd tegen spambots. JavaScript dient ingeschakeld te zijn om het te bekijken.. You will find more information about XPure’s product portfolio and services on www.xpure-systems.com.

Ascorbic acid was discovered in 1928 by Szent-Györgi. Commercially, ascorbic acid is mainly produced by a combination of synthetic organic steps and biotransformation. A well-known intermediate product is 2-keto-L-gulonic acid. This is produced from the sodium salt of the L-gulonic acid and has been acidified according to exact the same Ion Exchange route, as presented below for vitamin C.

In order to obtain the pure product, ion exchange is an attractive method for removing the salts.

The objective of this application note is to demonstrate the feasibility of the continuous ion exchange for removing Na+ from the sodium ascorbate. The feed flow consists of an aqueous solution containing Na-ascorbate. The sodium is exchanged by H+ on a strong cation resin in the H+ form. The resin is regenerated with HCl.

2-keto-L-gulonic acid (precursor to vit. C or ascorbic acid)

Ascorbic acid (vitamin C)

Design Considerations

The sodium form associated with the Asc (ascorbic acid) would be exchanged for a H+ thus forming ascorbic acid on a strong acid cation resin with 1,8 eq/l (expressed in terms of equivalents per unit volume of packed bed) maximum capacity.

The entire operation is executed in a XPure carousel system with 20 to 30 columns.

Process description

The overall manufacturing process is schematically summarised in the next diagram Figure 1:

Figure 1. Flow diagram for vitamin C manufacturing

For the Ion Exchange step we focus on the acidification step to vitamin C. This is in fact a purification step, see below Figure 2.

Figure 2. Conceptual design of continuous IX purification for (Product) vitamin C. Each block may contain multiple columns. Total number of columns typically 20-30.Note: yellow lines indicate water flows within the system

The regenerant involves hydrochloric acid implying that NaCl is the target compound to remove in the subsequent wash steps. Caustic is applied for intermittent regeneration and protein removal.

In an experimental study it has been found that residual Na-ascorbate is more difficult to remove (ads wash) than NaCl (regen rinse), the ascorbate obviously shows affinity to the resin surface.

Water consumption is an important process parameter. In order to save on water, a counter current contact concept has been applied. This can be accomplished by assigning multiple columns to the wash&rinse zones. The next Figure 3 shows the effect on water consumption –expressed in BedVolumes- for 4 different configurations. Please note ideally 0.3-0.5 BV (“interstitial volume” or void fraction) would be sufficient for 1 column displacement.

A multi-column carousel system can easily, and relatively cost-effectively accommodate a counter-current contact zone.

The dilution in the vitamin C process typically is 20%-35%. This is significantly lower than fixed bed processes in which 2-fold dilutions are not exceptional.

The conversion of Na-ascorbate is at least 99.5%. . The water consumption, without using the possibilities to re-use water in the process is about 15 liter per kg Vitamin C. The hydrochloric acid (7 wt%) consumption is 5.4 liter per kg vitamin C, taking into account an excessive use of 20%. The caustic consumption should be fine-tuned to the protein content of the feed solution and can be minimised by optimising the intermittent caustic wash. Losses of product in the caustic wash and contamination of the product stream with chloride are minimised by carefully designing the adsorption wash and elution wash sections. Product dilution is minimised by applying an entrainment rejection zone.

One of the dominant factors in the operating expenses for ascorbate (and Na-2-KLG) acidification is related to the costs of the ion exchange resin. This can be related to the specific productivity of the system, which expresses the annual amount of product that can be purified per unit volume of resin. The productivity of a carousel system for the purification of KGA and vitamin C typically is higher than 800 tpa/m3. Productivities in fixed bed processes may be a factor 5-10 lower.

Platform molecules form the basis for several formulations in chemical, food and pharmaceutical industries. Lactic acid (LA), a 3 carbon carboxylic acid is one such platform molecule. LA has a broad application field ranging from food industry to polymer production. Complying with the traditional philosophy of demand vs scale vs cost, a cumulative annual growth rate > 20 % for LA drives the need for cost effective and efficient production processes to meet the demand.

LA is produced by both chemical synthesis and fermentation, where fermentation has been the preferred choice due to enantio-selectivity and environmental sustainability factor. However, fermentation based processes require highly efficient downstream processing (DSP) for removal of impurities and to enable the claimed environmental benefits. Because, if DSP is energy intensive, then sustainability can become questionable. Further, DSP also contributes to > 50 % of overall cost of goods (COGs) which can define the business model. In this application note, we will discuss how use of simulated moving bed (SMB) mode of ion exchange adsorption (IEX) steps can influence the overall COGs.

Figure 2: Major sub-processes integrated to produce lactic acid

LA production process involves both cation and anion exchangers to remove positively-charged cationic impurities and to capture LA, respectively. These two steps use industrial resins, which are known for their robustness, high exchange capacity and long process life. However, operating these resins in batch mode result in partial utilization of the resin capacity and requires larger columns, high amount of buffers and waste streams.

This scenario leads to low productivity, less sustainable process and increase in process costs. Therefore, the SMB technology can successfully be applied in this scenario, to develop a more sustainable process with reduced costs. This is due to the fact that SMB results in better resin utilization and lower buffer usage leading to reduced operating costs. Additionally, improved product titers in case of SMB can reduce the scale of unit operations used post SMB.

In the traditional scenario of switching from batch to SMB, the IEX costs can be reduced by 30-50 %. For example, in a lactic acid purification process, where IEX step can contribute to about 20 % of overall DSP COGs, the SMB technology can reduce the DSP COGs by 5-10 %. This improvement in process economics can be critical for fermentation based products like LA, which competes with petrochemical products. An estimated cash flow analysis for LA production process with batch and SMB IEX systems is depicted below. Here, a 32 kt/a plant capacity is assumed, with an OPEX of about 915 €/t, CAPEX of about 21 M€ and a sales price of 1500 €/t. Shifting from batch to SMB in such a scenario can reduce the breakeven period from 3.25 to 2.75 years. Thereby enhancing efficiency, sustainability and profitability.

Sugar is produced in many countries all over the world. The term “sugar production” relates to various products, primarily mono- and disaccharides.

There are two widely applied large-scale chromatographic carbohydrate (sugar) separations: the isolation of the disaccharide sucrose from molasses and the separation of the two monosaccharides fructose and glucose (figure 1).

Figure 1: The structure of fructose (left) and of glucose (right)

Sugar refining

Monosaccharides like fructose and glucose are produced mainly from beet, cane or corn. After several refinery steps including milling, filtration and hydrolysis, a mixture containing glucose is obtained. Glucose is isomerized using immobilized enzymes, to the much sweeter component fructose. The composition of this equilibrium mixture ranges from 50/50 to 45/55 (fructose/glucose), and often contains up to about 8% of oligosaccharides.

This mixture is separated by chromatographic separation into a fructose-rich and a glucose-rich component. The dry matter content of the feed flow varies up to 60%w/w.

The resin material used in fructose/glucose fractionation is a gel-type sulfonated polystyrene-DVB strong acid exchange resin in the calcium form. The separation is based on the preferential adsorption of fructose, which forms a complex with the calcium ions. This chromatographic method is called Ligand Exchange Chromatography (LEC). There are several commercially available resins for this application.

A secondary phenomenon is that larger molecules, i.e. higher oligosaccharides are not able to physically fit into the resin pores. The mechanism of separating large molecules from small molecules by preventing some of the large molecules from getting inside the stationary packing is called size exclusion chromatography. Size exclusion chromatography takes place simultaneously with ligand exchange chromatography in the purification of fructose. This results into larger oligosaccharide concentration to leave in the raffinate phase. Size exclusion can also be exploited in the separation of higher saccharides from monosaccharides.

Both components are recovered for over 90% and the purity of the product flows is above 90% as well. Glucose is recycled and re-isomerized; fructose is sold as a pure product or mixed with the equilibrium mixture mentioned above to yield high-fructose syrup. The fractionation process takes place at 60°C, to reduce microbial contamination and to reduce the pressure drop by lowering the dynamic viscosity of the liquid.

SMB Chromatographys

The chromatographic separation of fructose and glucose can be efficiently done in a simulated moving bed (SMB). Figure 2 shows experimental data from a glucose-fructose fractionation in a SMB system. It also shows the predicted performance from our process design software.

Figure 2.Comparison of production data of fructose/glucose fractionation on a 12-column system with calculations according to our process design model

The same fractionation mechanism applies for lots of other applications,

often directly related to sugar processes where C5/C6 sugars are involved,

or indirect sugar processes where sugar lies at the basis of a fermentative route to produce biomaterials like organic acids, (residual) saccharides and amino-acids.

This blog will present a new development regarding the application of Expanded Bed Adsorption (EBA) technology for small molecules.

Amino acid – Gamma-aminobutyric Acid (GABA)

Biotechnological fermentation processes are nowadays common in the industry to produce a broad range of biological molecules. Obviously, the bio-based industries need efficient, cost effective, downstream solutions to process these complex streams.

The topic for this blog is the purification of small molecules like amino acids from unclarified bacterial broth using a combination of different technologies. To date the use of Expanded Bed Adsorption (EBA) for processing unclarified broth is state-of-the-art technology and its description can adequately be found in literature. In an EBA column, the resin bed is expanded by upward feed flow and the (then actuate) bed void allows particulate biomass to flow through the resin bed and selectively capture target molecules. This makes dedicated clarification steps such as centrifugation and filtration redundant. However, a further improvement of the technology that has been regarded feasible, is integration of EBA with the simulated moving bed (SMB) technology (Ref. 1). To address this challenge the purification of a model compound, ɣ-aminobutyric acid (GABA) was investigated.

What is new: use of geltype adsorbent in Eba mode processing

Resin selection is one of the critical aspects of developing an EBA process. Relevant resin hydrodynamic properties include particle diameter and density. Typically, these beads are agarose-based and have a heavy core. Only a few specific EBA resin types are available, which are also quite expensive. These aspects are major hurdles for the application of the EBA technology in manufacturing of bulk chemicals where low production costs are key.

The current study focusses on the purification of ɣ-amino butyric acid (GABA) from a bacterial, E. coli, fermentation broth. It is known that strong acid cation exchange (SAC) resins exhibit selective binding of GABA (Ref. 2). The resin screening for current investigation was not limited to specific, porous EBA resins. Surprisingly, it has been discovered that gel-type (non-porous) resin(s) could also be used for EBA applications; although the density is at the low end (e.g. 1.2 g/mL) linear flow rate up to 600 cm/h were attained. In this case, industrially available resin type (Finex, CS16GC) is furthermore characterized by high ion exchange capacity (e.g. 1.6 eq/L). In Fig. 1 pictures of gel-type and macroporous-type polystyrene resins are shown.

Fig. 1 Text see last page

GABA purification and eba-mode processing

First, the GABA purification process using the gel-type strong acid cation exchange (SAC) resin was defined for a “single EBA column process”. The following process steps were identified:

Adsorption (loading GABA-containing unclarified broth)

Wash (H2O)

Elution (NaOH)

Wash (H2O)

Regeneration (H2SO4),

Wash (H2O)

Obviously, critical process requirement for EBA processing (e.g. maintaining the target bed expansion) should be fulfilled. Important parameters incl. buffer concentrations, target buffer volumes and flow rates were established. Flow rate ranges for individual process buffers and unclarified broth were studied and optimized to prevent the occurrence of unwanted changes in the expanded resin bed. Detrimental for EBA process in SMB mode is the overflow of resin from the column top resulting in loss of resin or even clogging of valves.

Technology integration: EBA in SMB mode

For the integration of EBA and SMB process, a state-of-the-art 8-column lab scale system has been designed and built (see Figure 2). Important feature is the flexibility to define the operating conditions per column. Within the software, recipes can be generated that address

the total number of columns in a SMB cycle

number of column positions

inlet and outlet valve configuration per position

pump flow rate

sensor control and

switch time per position.

As mentioned, a critical aspect is to ensure optimal bed expansion. For this purpose, ultrasound sensors were installed at each column outlet that measured the expanded bed level. By this measurement, the software controlled the pump flow rate to maintain the desired bed expansion for the individual columns. The pH profile of the product stream exiting the different SMB columns passing through the elution zone was assessed to represent consistent product quality at a cyclic steady state of operation. The quality was defined by removal of biomass and other soluble impurities (Ref. 3).

Fig. 2. Text see last page

Conclusion

The promise of reduction of unit operations, increased product yield and productivity and reduced buffer consumption using EBA technology for complex feed streams has been recognized for many years. It has now been demonstrated that further process improvement by integration of the EBA and SMB technology for purification of an amino acid, GABA, from unclarified bacterial broth was successful. A relevant factor is the use of gel-type resin (CS16GC) exhibiting a higher binding capacity as compared to that of macroporous resin. The integrated one-step EBA-SMB process resulted in a GABA purity of ≥ 92% and > 98% removal of biomass. The results show that integrated EBA-SMB technology enhances process efficiency and economics of bioprocesses. It is anticipated that further improvement can be realized by increasing the number of columns.

EBA-SMB: one unit operation

The use of Expanded Bed Adsorption (EBA) for the purification of biological molecules from unclarified harvest is well described for many applications in literature. The advantages are obvious; including shorter process time, higher yield, low buffer consumption, and no additional clarification step.

The next step to further increase the productivity within e.g. bio-based industries is integration of EBA with Simulated Moving Bed (SMB) technology in one single unit. For this application, multiple EBA columns need to be connected to each other in order to obtain the full advantage of processing in SMB mode. Important differences as compared to packed bed column chromatography are that

the resin particles in the EBA columns can move freely and

the resin particle movement and behaviour in the EBA column is highly dependent on resin properties, inlet flow rate.

The Challenge

The main challenge is to prevent collapse of the expanded resin bed or a sudden increase of the resin bed level resulting in loss of resin particles at the column top outlet.The latter may happen when the density and/or viscosity of unclarified broth is significantly higher than aqueous process buffers. It is evident that processing of high viscous (feed) solutions result in a (much) higher resin bed expansion as compared to aqueous solutions at the same flow rate. Both occasions; a too low bed expansion or too high expansion are potential obstructions to properly execute EBA processes in SMB mode.

A very tight control of the expanded bed level is therefore mandatory for EBA executed in SMB mode

Expanded bed level control is crucial

A number of strategies can be applied to keep the level of the expanded resin bed constant during processing of unclarified broth.

Full automatic feedback on the feed flow rate using a target expanded bed level.

Automation using a) expected flow rates for the individual steps in the process combined with b) target expanded bed level.

, In case of well defined process characteristics regarding target expansion and expected flow rates, . no or only limited feedback on the feed flow rate maybe applied

The third option requires profound process knowledge. The behaviour of the resin bed expansion as a result of change in flow rates and consecutively applied different feed streams and buffers need to be known in order to develop a proper strategy for controlling the EBA process. Furthermore, it should be taken into consideration that time and volume required to achieve both the required expansion and an effective process step may constrain each other.

Development of EBA-Smb process

Using well-characterized feed streams, it is worthwhile to anticipate on the expected changes of expansion brought about by the consecutive processing of unclarified broth and different process buffers. Three parameters are relevant a) required volume per step, b) flow rate and c) viscosity/density.

(a) Make an assessment of the number of settled resin bed volumes (BV) needed for the execution of the EBA process. This can be done based on a regular packed bed chromatography process. It must be recognized that the displacement of particulate containing material does take more rinse volume in EBA mode.

(b) Establish the flow/expansion behaviour of the unclarified broth and all process buffers. This will give a reliable indication of the flow rates that need to obtained for each process step.

(c) Establish the behaviour of the expanded bed during the transitions between unclarified broth and process liquids.

Crucial is to know how the expanded bed responds to the change to a feed stream with a higher viscosity (for instance unclarified broth). Loss of resin from the column top may occur if the flow rates remain too high. This is particularly relevant in case the EBA process runs in SMB mode. At a worst case scenario the resin particles may block valves and tubing and damage the system.

Below, an example is given how the expanded bed level can be kept in a narrow range during the transition from an aqueous solution to a high viscosity solution just by changing flow rates in a smart manner.

Easy control of expansion feasible?

Polyvinyl alcohol (PVA) is used as a model compound to mimic a high viscosity feed stream (i.e. “unclarified broth”).

First, the flow rates have been determined to obtain the target expansion of 1.85-fold for water and the viscous PVA solution (i.e. 610 and 344 cm/h, respectively). Thereafter, it has been investigated how the expanded bed responds to the transition from water to the PVA solution. Figure 1 shows what will happen when the flow rate is directly switched from 610 cm/h to 344 cm/h upon changing to PVA: a sudden sharp decrease of the expansion is observed within 0.5 BV. Not earlier than after 3 BV the expanded bed reaches the target 1.85-fold expansion. This is an undesirable situation. An unstable bed may result in suboptimal flow distribution and mixing of the supernatant.

Fig.1 (see text last page)

This is prevented by initially doing nothing i.e. just keep the flow rate unchanged upon the switch to PVA. As shown in Figure 2 there is a substantial delay of the bed expansion to respond to the PVA solution. By keeping the flow rate unchanged for 0.5 BV the collapse of the expanded resin bed has been prevented. Interestingly, a first change in flow rate (i.e. 400 cm/h), followed by a second change to the final flowrate of 344 cm/h during the transition has a major effect on the resin bed expansion: undesirable changes in the resin bed expansion have been prevented.

Fig.2 (see text last page)

Conclusion

A development strategy for processing unclarified harvest in EBA-SMB mode has been presented. By taking the delay of the expanded bed to respond to changes in viscosity into account, simple programming of flow rates and volumes for the individual process steps prevent significant changes in resin bed expansion. As a result, the resin bed expansion remains within a 90% – 110% range of the target bed expansion and enables the successful processing of complicated feed streams in EBA-SMB mode.

Figure 1

Impact of a 1-step decrease of flow rate on the resin bed expansion in case the flow rate is changed directly upon switching to the PVA solution (“unclarified broth”).

Figure 2. .

Impact of a 2-step decrease of flow rate on the resin bed expansion in case the flow rate is changed after 0.5 BV after switching to the PVA solution (“unclarified broth”).

At XPure, we believe that the application of efficient downstream technologies like EBA leads to sustainable and profitable process industries. Here, we would like to share the thoughts of a young scientist from TU Delft, about his work on EBA Technology and award-winning talk at ESBES 2018.

How do you feel about winning ESBES (European Society of Biochemical Engineering Sciences) award for 2018

I’m really happy as a Ph.D. candidate in Bioprocess Engineering at Delft University of Technology, that I was able to participate and selected as one of the winners. At the previous ESBES in Dublin two years ago I saw two of my colleagues present during the award ceremony. Since then I’ve been looking forward to a change to participate and be able to share my story with a bigger audience.

What do you think made you stand out among the high-quality research presentations from different streams of biochemical engineering?

In the group of Dr. Marcel Ottens, I strongly feel that our approach in which we applied traditional chemical engineering techniques together with mathematical modelling to a high potential technology like expanded bed adsorption (EBA) helped me to stand out.

How do you see the future of EBA?

Here I must say that I’m really excited about the approach to EBA Xendo has within the European PRODIAS (PROcessing Diluted Aqueous Systems) project. So far the application of EBA in biopharma has been challenging, as investments on technologies which can have a small level of discrepancy can lead big risk factor. Also, cleanability (and with it the validation and compliance challenges) is a very critical aspect for pharma and one of the fundamental challenges. The fields of non-pharma proteins and small molecules have different drivers for process development and CAPEX/OPEX optimizations are more dominant. I think here EBA can be a competing separation technology. In turn, successful business cases based on EBA will help convince industries that might have become reluctant to implement it.

What do you see as challenges to be addressed that can prepare the technology for future?

In our research (which is part multi-disciplinary consortium) we focus on the fundamentals of fluidization in EBA columns. We try to approach it as a liquid-solid fluidized bed rather than a packed bed column “in disguise”. Since experimental research on hydrodynamics for such a system is highly challenging, we use advanced computer simulations. These allow us to investigate local resin particle environment as well as extract statistics for the overall expanded resin bed. Developing these models has proven to be a tough challenge but are now at a point where we can generate reliable data. Our aim is to use insights we get from the simulation data for the better design of column hardware and to provide a benchmark for ideal fluidization behavior. These benchmarks can then be used to detect early deviations in the process. We hope that this increases the rationale in process control, leading to a more robust equipment operation.

Brief motivation for researchers out there.

Development of EBA systems is a field dealing with multi-phase, multi-scale and multi-physics challenges. Typically, processes at various length and time scales will interact with each other in ways that may not seem obvious at first. These are challenges which, on a more abstract level, are not unique to EBA and I think lessons learned here can be applicable to a broader range of technologies. Continuing that line of thought I’d like to end with a quote from Sir Stanley Eddington I recently came across.

“we often think that we have completed our study of one we know all about two, because ‘two’ is ‘one and one’. We forget that we still have to make a study of ‘and’ ”

Innovation through hybridization/integration of technologies is a well-known approach. This approach has been effectively applied to achieve specific process objectives in chemical, biochemical, food and pharmaceutical industries. The approach can include either two separate units operating in tandem or as a single integrated unit. Membrane operations are usually found in tandem with other unit-operations for recycling cells during fermentation or buffers in case of downstream processing. In integrated operations, the overall efficiency is achieved by using two or more operating principles in parallel. Reactive distillation, pervaporation, fermentation with in-situ product removal through stripping etc. are some examples of integrated unit-operations. The current article briefly discusses one such integrated unit-operation called Simulated Moving Bed Reactors (SMBR).

SMB technology has proven to enhance the efficiency of chromatography/adsorption separation through continuous counter-current operation. This principle can have a similar impact on heterogeneous catalytic reactors with catalysts immobilized on support beads or adsorbent and packed as a fixed bed or fluidized bed. The countercurrent effect of SMB is known to enhance the performance of equilibrium driven reactions and mass transfer kinetics, whereas the continuous mode of operation helps in achieving improved productivity. Therefore, SMBR can find its application as a techno-economically viable process solution.

Fundamental phenomena during heterogeneous catalysis are mass transfer (MT), reaction and inhibition kinetics. MT is more critical in case of a catalyst on solid support and substrate dissolved in a liquid system. However, the difference in MT kinetics of a substrate and inhibitor can also be applied as a separation principle to maintain or improve catalytic efficiency. For example, consider a catalyst exhibits product inhibition at a specific product concentration and it is identified that the substrate and product have different characteristic times at which they flow through the column. If the characteristic time difference in a batch reactor is not sufficient to minimize product inhibition, an SMBR can help in increasing the difference through the countercurrent effect. Thereby enhancing step efficiency and process economics.

Resin is an integral part of any chromatographic process and often a big cost factor. Over time, the resin will deteriorate until it reaches the point where it needs to be replaced in order to maintain an economically viable process. As resin can be costly, you don’t want to replace it too early but predicting exactly when you should this can prove to be difficult when you're developing new processes. When the resin gets exposed to new combinations of products and chemicals, its lifetime may vary and you might need to replace it after 250 production cycles. Or maybe after 500? Or can the resin still deliver after 2000 cycles?

Without experimental data to back up the resin costs, it's quite difficult to write a robust business case for chromatography; the XPure-R is our answer to this challenge. The system enables you to age up to 10ml resin under your process conditions in a fully automated and time-efficient manner and can be tested in both fixed and expanded bed (EBA) mode.

XPure-R allows you to focus on your other research and will age your resin because it was designed to operate without attendance. All you need to do is prepare the XPure-R by supplying all the required process liquids, programming the recipe, and press run.

It is also possible to outsource your resin aging studies to XPure, saving you even more time.

Examples:

The cycle time for an investigated process was reduced from 1 hour and 33 minutes to 7,5 minutes; a 92% reduction.

For a resin aging experiment of 1000 cycles, the XPure-R reduced the experimental time from 64 days to only slightly over 5 days.

A shift from batch production to continuous production requires a different approach in terms of process control. Especially when the continuous chromatography is, in essence, a rapid sequence of “batch” operations with specific conditions for each process step. Combine this with integration of the unit operation in a production chain, process control quickly becomes critical. With several real-life examples of how control within an SMB can be applied, this blog will look into the different levels of process control for continuous chromatography and how they work together to ensure an efficient process. These examples cover the impact of the impact of variation in processes due to flow rate control or sensor based progression on cycle times and how to mitigate this impact and ensure steady state.

Simulated Moving Bed (SMB) Chromatography is a continuous form of chromatography that seeks to enhance the separation efficiency of chromatography while reducing operating expenses such as resin inventory and buffer consumption. There are 2 different types of SMB system available; the carrousel SMB and a valve matrix-based or static SMB. This blog is mostly aimed at valve matrix-based SMBs, but parts of this blog can also be applicable to carrousel SMBs.

Before running an SMB you have to decide how you want to control it: synchronously or asynchronously.

As the name implies, in a synchronous process all columns move through the process at the same pace. A carrousel SMB is a great example of a synchronous SMB as all columns move to a new position after a predetermined switch time.

An asynchronous process gives a lot more opportunity to control the process. It is possible to break down the process into a series of positions, where each position has a detailed set of instructions and conditions. A column can only progress through the process as soon as it has completed these set conditions. This approach places more control and responsibility in the hands of the process engineer and the control strategy.

As with any continuous process, it is important that the process is controlled in such a way that the desired steady state is obtained and maintained. At steady state, the continuous process is performing at the intended efficiency and any deviation from this will impact overall process efficiency and economics. The process control and strategy should, therefore, be able to handle deviations that could disturb the cyclic steady state of an SMB.

For an SMB process, the progression of columns through the various positions within the process is conducive to the steady state of the process. The condition for a column to progress can be based on time but also on different parameters such as pH or conductivity. An example of such a step is an elution step. In the elution zone, it can be economically attractive to stop collecting liquid to the elution stream when the product concentration in the eluent becomes too low and would cause dilution of the product stream. When letting an inline parameter control the progression of columns, time becomes a secondary progression condition and thus variation in switch times could occur. The control strategy should be able to ensure steady state when this occurs.

Control strategy becomes even more important when SMB technology is hybridized with other technologies such as Expanded Bed Adsorption (EBA). As both technologies in a hybridization have their own specific set of requirements, the control strategy will need to be able to handle both technologies. To expand slightly on the EBA technology, this is a chromatography technique where the liquid flows in an upward fashion. This allows particulate matters (e.g. cells, cell debris) to flow through the bed without clogging. As the adsorbent is pushed up by the liquid flow, care needs to be taken that the bed level of the resin is monitored or controlled and that the adsorbent does not wash out of the column. An example of such a system can be seen in this article.

THE 5 LEVELS OF PROCESS CONTROL FOR SMB SYSTEMS

Figure A: the 5 levels of control within an asynchronous switching, optimised SMB setup

Level 5: individual columns

In processes where a certain set of conditions within a single column are needed to ensure the desired process efficiency, it is important that the control system can react to potentially detrimental effects down on a single column level.

Control of conditions within the column use sensors directly connected to a column to control a parameter within the column. To illustrate this, in an EBA setup a bed level sensor can be used to ensure that the resin bed expands appropriately but does not expand too much and overflow out of the column. The sensor would control the bed level by controlling the involved pump(s).

Level 4: Zone level control

It is possible for an SMB to have multiple columns located in a zone. The column configuration can be both parallel and/or serial. In parallel the liquid stream is divided over the columns in parallel, effectively dividing the flow rate and increasing contact time. When the columns are in a serial configuration, the liquid is fed from the outlet of one column to the next.

When a zone has been configured with a parallel or serial configuration, the control strategy should ensure that the columns in the zone are only receiving fluid when the zone is populated with the required amount of columns. Therefore, it could be possible that two columns are “waiting” for a third in a zone requiring three columns. “Waiting” in this context would be that there is no liquid flow through the columns until the run condition of three columns is fulfilled.

Within a zone containing multiple columns, it should also be possible for a sensor to be able to influence the process. An example of this could be a zone with three columns linked in series. When product dilution in the product stream is undesirable, you would want to stop elution collection once a certain product concentration is reached. This means that a sensor connected to column three controls the outlet valve of column three, effectively controlling on a zone level.

Level 3: Inter-zone control

Little control is required in zones where time is the main controlling parameter. As discussed previously, it is possible for a zone to be controlled by different parameters such as time, pH, conductivity, bed expansion and UV absorption. In zones where other variables are the controlling parameter, time becomes a variable that could potentially affect system steady state if inappropriately controlled.

As the cycle time for the columns needs to be equal, the variation in position timing needs to be compensated. To compensate in a fixed bed SMB, a column can be parked in a waiting position. This means that the valves to the column are closed and that there is no liquid flow through the column. In an EBA-SMB, there is the added complication of having the expanded bed which potentially cannot recover if it collapses after, for example, the feed zone. In this case, the compensation positions are used to keep the bed expanded and are a prelude to the next zone.

Process optimization for both SMB and EBA-SMB systems is done in such a way to minimize the duration of any waiting position. The aim of these waiting positions is purely to ensure a cyclic steady state.

Level 2: SMB level control

The SMB as a singular entity also requires control. For a carousel SMB, this control is simple as only pump speeds and switch times need to be controlled.

As discussed above, a valve-based SMB allows for many more degrees of control enabling potentially higher levels of efficiency but requiring more rigorous process design. Depending on the requirements of control at column, intra-zone and inter-zone conditions, the SMB control can be simple time-based switching or integration of several levels of control.

Level 1: Inter-unit operation control

As the SMB is dependent on upstream and downstream unit operations to receive and discharge liquids, it is important that it is clear how the SMB should react to changes in the process. When upstream unit operations produce faster, the SMB may need to speed up its production speeds. The same holds true that it may be necessary to slow down the SMB production speed if downstream unit operations are disrupted. However, the range of flexibility to speed-up and slow-down the SMB process is defined by the permissible deviations in efficiency, purity and yield requirements.

A comprehensive and holistic approach should be taken when designing an SMB control strategy. Single column experiments can yield significant information on how to control on a single column level and provide enough input for an initial SMB design. For further steps however SMB experiments would be required, to allow for fine tuning on higher levels of control.

Scenarios for inter-unit operation control for an SMB need to be determined from a good process understanding and then be tested to confirm appropriate SMB performance.

Recently, we brought one of our customized VANMOOF bikes to this year’s ACHEMA. As always, the bike attracted a large crowd and we wish to congratulate this years' winner and Wim Vermeire, Director Production DSP at Citrique Belge! We hope that you enjoy it! If you’d like to see where you can win the next XPure bike and learn about SMB and EBA technologies subscribe to our newsletter!

There are quite a few excellent textbooks that cover the design of separation processes, this also applies to adsorption chromatography processes, the subject of this blog. The majority of these books, however, deal with the design process from a rather academic approach. Most of the time, too little attention is paid to the specific product requirements and market or client specifications to be complied with.

Moreover, most often the design information is not readily available.

The reality is a bit more complicated and the majority of information required for designing an SMB operation has to be derived from column tests, estimated or correlated.

BASICS OF DESIGN PROCEDURE

Any design procedure is an iterative process, it starts with some essential considerations

Can the (target) product be purified

Is it feasible and thus easier, to design an adsorption process for removal of impurities

Is fractionation a better alternative when dealing with poor binding properties of either the target molecule or impurities

Is conversion of the target molecule the case, for example dealing with acidification of organic acid conjugates.

Next items to thoroughly think about are feed properties, process capacity, and product requirements.

Plant factor. A continuous adsorption process should be designed as full continuous 24h/day. If the upstream process is a (semi-)batch process, one should base the design capacity on a time-average feed production rate

Maximum feed capacity, it is noted that a continuous adsorption process can be easily be downrated by simply slowing down the cycle time and related feed, wash and buffer consumption rates. So it’s best to design and configure a system based on the maximum (future) expected feed capacity

Feed properties, like density, viscosity, stability, particulates, and temperature. Mass transfer kinetics are influenced by temperature and viscosity, and also by flow velocity in the resin bed. Particulates may disturb the bed stability and flow distribution and should, therefore, be avoided

Last but certainly not least, requirements like product purity, yield and concentration are of tremendous influence on the design. Concentration has a substantial effect on further downstream process costs, e.g. evaporation/crystallisation and drying.In general, in case it is required to attain purity levels beyond 98% the costs of processing will exponentially grow

SEQUENCE OF THE DESIGN PROCEDURE

Iterating to an optimal process design, it is important to look at:

Process chemistry, this is the resultant of combining feed and buffer (eluent) properties, with an appropriate resin, having the best adsorption performance

Kinetic parameters, these can be derived from literature or column tests. In the process model calculations, a 2-film model featuring diffusion from bulk to film, respectively from liquid film to stationary phase film has been applied. The model also contains correlations from published experimental data

For 2 and 3 most of the time good and reliable information can be obtained by column tests. Often an industrial scale batch chromatography process already is in place which data could be of tremendous value when it is considered to change to a continuous process.

PROCESS DESIGN

A conceptual SMB configuration contains a number of zones. A zone is defined as a part of the overall process flow diagram in which the flows through all applicable columns are equal. The conceptual configuration displays these zones in terms of a block diagram with the interconnections between the zones.The figure below shows an elementary conceptual design for the most simple bind & elute chromatography system. It contains 4 zones:

Adsorption

Elution

Adsorption wash

Elution rinse

In the conceptual design phase, the following zone may be considered

To apply diluted adsorption section (same applies to elution zone). The advantage of adsorption wash recycle is that entrained feed liquor will be recovered and moreover it saves an additional side-stream. It should be noted that the sorption isotherm must show adequate binding capacity in the lower feed concentration regime to make diluted adsorption advantageous.

Entrainment rejection (upstream) adjacent to either adsorption or elution zone. This enhances the depleted feed or the elute (often containing the product) effluent concentration

Regeneration zone. This may be necessary to bring back the IX resin into the adsorption condition. Or, in other cases, to remove residual impurities after the elution.

Equilibration zone. After a regeneration or elution, the equilibration buffer brings the chromatography resin into the right condition to resume adsorption

Upflow wash zone in case the feed solution contains particulates. An upflow wash should, therefore, be considered after the adsorption wash step.

An SMB configuration displays how the sequence of process steps is included in the SMB process cycle. The concept doesn’t specify the number of columns (per zone) yet. This is one of the essential parameters that needs to be iterated in the detailed design process further on.

This iterative process concludes with a detailed design featuring:

Performance indicators: yield, purity, and recovery

Hydraulic indicators like pressure drop and flow velocities in both resin vessels and connecting piping.

To conclude the figure below shows a typical process flow diagram for a bind and elute IX-chromatography system. It features a diluted regeneration zone as well as additional upwash to remove any particulates that may be trapped in the feed adsorption zone.

EBA chromatography effectively addresses the critical challenges of packed bed chromatography. It reduces e.g. clarification operations prior to the columns resulting in lower costs and improved yield. Minimal back pressure enables to achieve optimal scale of operation and productivity. The XPure-E system has been designed and built to perform EBA chromatography operation in a smooth and controlled fashion enabling:

Process development with enhanced scalability and operability

Handling viscous and turbid feed streams which are difficult to process through membranes or packed beds

Intensification of Process Development using a Design Based Turnkey Solution: a case from SMB Chromatography.

Rapid technology development and an increasing number of technologies entering the market are setting the bar high for their successful application. This is no different for separation technologies. How does a design based turnkey solution help in successful application of novel technologies? A case presented, based on SMB (simulated moving bed) technologies and intensification of SMB process development.

Background

SMB is an industrially proven technology, which can improve the efficiency of adsorption/ chromatography based processes by enabling continuous processing, better resin utilization, reduced buffer requirement, improved yield, purity and productivity with a compact footprint of equipment. However, these benefits do not proportionally indicate the extent to which SMB technologies are currently applied or even being investigated at a process development stage. Major factors leading to this situation include limited availability of:

System that can represent an appropriate scale-down model for an existing or to be developed industrial scale operation

System which is easy to set-up, CIP, maintain and modify in short time

Process control which is flexible to process integration and enhances operability

These limitations not only inhibit successful application of SMBs but also reduce the efficiency during process development stage.

Solution

It is clear from the problem background that it is essential to provide a turnkey solution that enables investigation of SMB technology under diverse process development scenarios overcoming the current limitations.

Stages of technology investigation and optimization during process development

Technology investigation and optimization as shown above consists of four major stages. Therefore, proposed turnkey solution needs to be flexible to aid at any of these stages.

The solution contains 4 parts, which form a package that can aid in SMB technology testing and implementation during process development:

A design-based approach is proven to improve the efficiency of a development process. A regular design tool for process technologies involves input from the user, iteration of design equations and provides an output. Therefore, it is essential to define the appropriate input parameters and fundamentals that allows the tool to provide a representative output taking into account all the process performance attributes. To obtain such a design tool for SMB, we propose a parameter sensitivity based approach. In this approach, the design tool involves a sensitivity analysis prior to the design iteration, where you can identify the critical process parameters for the specific process scenario. Based on the outcome of sensitivity analysis, the design tool provides the flexibility to enable additional input parameters and iterations or eliminate redundant parameters and functions for a specific process scenario. This way, the tool can filter the SMB designs for a broad range of applications and at the same time guide design-based optimization. This can potentially enhance the freedom for process developers from different fields of application to investigate SMB as a potential alternative before deciding on further

The design outcome is used to build an appropriate scale-down model which not only takes into account all the critical process parameters but also provides an operating window for further investigation and optimization.

Stage 3 is highly critical in case of SMB, mainly because an SMB operating window can involve a range of column numbers and operating conditions to be experimentally investigated using a lab scale system for determining the optimum. Therefore, it is important to design and build lab systems, which are flexible to mechanical modifications. The desired mechanical flexibility directly translates into the requirement for automation software that is highly flexible to implement additional changes and features based on process demand.Along with the process concerns, the practical concerns to set-up and maintain the system with minimal effort need to be addressed during system design stage. This can be done by dividing the system design and construction into several layers with corresponding options for customization at each layer and detailed outcomes related to both process and practical concerns. As a result, a system that can be readily deployed to determine the optimal operation and automation strategy can be

When all the above stages are integrated, a scale-up design can be obtained with relatively high accuracy as the above 3 stages give clear indication on critical aspects for large scale implementation

Conclusion

All the four stages discussed, when integrated, can provide a turnkey DSP solution for SMB process development as it will allow you to design, validate and scale-up SMB systems for diverse process scenarios. Thereby enabling successful investigation and application of SMB technologies. This design-based approach, when implemented for other process technologies, can enhance the overall efficiency of process development in terms of time, process detailing and performance, without requiring major additional investments.

This blog will present a new development regarding Expanded Bed Adsorption (EBA) technology. A turnkey solution is presented that makes feasibility studies using EBA easy.

Biological molecules

Biotechnological fermentation processes are widely used in industry to produce an abundant range of biological molecules (small molecules as well as large molecules, from amino acids to complicated monoclonal antibodies) which often need to be purified in order to meet high-quality standards. Examples of these fermentation feed streams include mammalian cell cultures, yeast and bacterial suspensions. Next to that plants like Tobacco are genetically engineered to produce recombinant proteins. These feed streams have in common that they contain particulates (e.g. cells, cell debris) and are hard to clarify.

In the diagram, the initial phase of the purification of a biological molecule is depicted. Several technologies (or combination of technologies) are commonly used to remove particulate material and isolate the molecule from the biological fermentation broth. For clarification the following technologies are widely used:

Centrifugation

Depth Filtration

Flocculation and depth filtration

Precipitation and filtration

Cross-flow filtration.

In general, a packed bed chromatography step is applied after clarification of the broth. Different chromatography resins can be used (including cation exchange resins and affinity-type resins) for a typical bind (adsorption) and elute process.

XPURE-E: Expanded Bed Adsorption

This purification process can be significantly improved using the Expanded Bed Adsorption (EBA) technology as can be observed on the right-hand side of the diagram. Whereas traditional column chromatography uses a packed resin bed, EBA uses an expanded bed. Particles such as whole cells or cell debris, which would quickly clog a packed bed column, easily pass through the expanded bed. Therefore, EBA columns can be used directly on crude harvests or slurries of broken cells, thereby bypassing initial clarification steps such as centrifugation and filtration.

The XPURE-E system operates with a closed-top column and therefore only one pump is needed to operate the EBA column. The system can be equipped with analytics including in- and outlet pressure, pH, conductivity, bed height and UV.

What is new: Active bed level control

The XPure-E system has been designed and built to perform EBA chromatography operation in a smooth and controlled fashion.

The most important feature of the XPURE-E system is the capability to monitor and control of the expanded bed level (bed expansion). This is important since an EBA process is run preferably at a predefined resin bed expansion. The level detector is integrated inthe top adapter of the EBA column and continuously monitors the resin bed level..

In the figure below is illustrated how the expansion of the resin bed (orange line) is monitored when the flow rate is stepwise increased from approximately 500 up to 850 cm/h (gray horizontal lines). The bed expansion factor is calculated by the software from the expanded bed height and the settled bed height.

As mentioned the XPURE-E is also designed to control the expanded bed level during operation. This is brought about via a feedback loop on the pump. The density and viscosity of different feed streams (incl. buffers) within one process may be different and may lead to changes of the resin bed expansion in case the flow rate remains the same. Therefore, the resin bed expansion needs to be controlled actively and kept constant within (narrow) ranges during the entire EBA process.

Active control of the expanded level during the process can be established in 2 ways:

Use of a setpoint value for the target bed expansion in combination with expected flow rate. This is especially useful when you are familiar with the process.

If not, you just need to fill in the target bed expansion and the system will increase the flow until the target bed expansion is reached.

In addition, it is also possible to operate the system without active level control. This feature can be used in case all feed streams are well defined and result in a predictable resin bed expansion at target flow rate.

The software platform allows the user to perform experiments in an easy and automated manner.

Easy programming

The XPURE-E is controlled by a comprehensive software package which runs using Windows operating system. Manual and recipe-based operation is possible all via a 10” touchscreen. The recipe is introduced into the system through a recipe editor (see the figure below).

It allows the user to define the process recipe including:

Up to 8 different zones in the process (equilibration, wash, adsorption, wash, etc.)

Flow rate, buffer volume and target bed expansion per zone

Different inlets and outlets

Active bed level control

The software calculates the expected process time per step and for the whole process. The intuitive graphic user interface gives the analyst an insight into the current state of the EBA process through various overviews. The data generated can easily be processed in spreadsheets such as Excell.

Conclusion

Performing EBA feasibility studies with the XPURE-E makes life easy:

It is the preferred technology to perform product capture and recovery step from complex feed streams, without requiring clarification or any intensive preprocessing steps

The use of EBA technology will result in increased product yield and productivity and reduced buffer consumption.

The XPURE-E system is easy to install and has high flexibility for lab scale operations

It is equipped with innovative automation and control with flexibility to evaluate design parameters and perform process optimization

If you’d like to investigate what EBA could mean for your processes don’t hesitate to contact us.

A comprehensive outlook on Industrial Biotechnology and its importance in Fourth Industrial Revolution (Expoquimia 2017, Barcelona)

The XPure systems team was recently present at Expoquimia 2017, in the beautiful city of Barcelona. We presented our new product XPure-E, which has been specifically designed for expanded bed adsorption (EBA) as part of the EU subsidized horizon 2020 project PRODIAS. This exhibition was organized in collaboration with WCCE (World congress for chemical engineering) and ECAB (European congress for applied biotechnology). At the expo, we had the opportunity to interact with experts in the field of bioprocessing from different industrial sectors, both upstream and downstream processing. In the current blog, we present an overview of discussions on major challenges industrial biotechnology is targeting to address, state of the art developments and implementation status and a conclusion on how XPure systems can aid in addressing the challenges.

Challenge groups vs Industrial sectors

Circular economy is one of the major challenges of the 4th industrial revolution which is involving breakthrough technologies developed from combination of physical, digital and biological advancements, in order to achieve the PPP (people, planet and profit) targets of several industrial sectors. Biorefineries and innovative bio-based solutions are contributing to circular economy both as a separate industrial sector and in synergy with traditional industries.

Healthcare and nutrition demands are continuously increasing with growing population, and changing environmental conditions are further posing new problems to solve. Quality and regulatory requirements add another dimension to technology development and implementation.

State of the art developments and implementation status

The role of large-scale industries is quite crucial to achieve circular economy due to the shear amount of mass and energy flows. At Expoquimia, key note speakers from several multi-national companies discussed their state of the art developments and approaches to fulfil the demands of circular economy with PPP solutions, it includes

Increase the number of novel biomolecules that can replace traditional chemicals

Along with capital, time is critical and therefore it is important to make quick decisions. For example, curves representing profitability vs value of compounds when produced using existing traditional vs biobased processes represent that low value molecules result in decreased profitability using biobased processes, which aids in business decision making. However, research should focus on changing this scenario (XPure systems is a potential technology in such a scenario with its ability to enhance profitability of low value molecules)

Gas fermentation which has been considered a farfetched fruit is now being implemented at a scale of 10,0000-120,000 m3/year, both in Europe and the US in synergy with steel plants, to treat waste streams in the form of syngas and produce ethanol.

Polylactic acid (PLA) and polyhydroxyalkanoates (PHA) from biobased lactic acid and polyhydroxy butyrate are growing to become platform molecules for several polymer industries. This reduces the carbon footprint generated by the traditional petrochemical based polymers like PET and PC etc.

Healthcare and nutrition challenges are identified to have more dimensions, some of the points include that

Existing process platforms are of major concern compared to capacities and therefore product and process development need to be simultaneous

Bridge between regulatory requirements and technology development is critical throughout the development process

Novel technologies like plant stem cells for cosmetics, nutraceuticals and API are being implemented at production scale. This method not only allows in selective production of target compounds, but also reduces the carbon footprint and water consumption considering that it requires fewer processing steps.

PRODIAS

The PRODIAS horizon 2020 EU subsidized project is developing technologies targeted at the above. Xendo is taking part in this project which is aimed at reducing the processing costs of compounds from renewable sources in diluted aqueous systems. PRODIAS targets on a holistic approach to develop upstream and downstream technologies meeting people, planet and profit demands. Xendo’s XPure systems (XPure-C/E/S) developed as a result can flexibly fit into the cost and regulatory model to achieve circular economy and meet demands of health and nutrition industry due to the following reasons:

In view of the talks by professionals from various fields of Industrial Biotech and diverse organizational roles, it is concluded that the strong demand to balance sustainable products and processes with desired profitability makes it essential to simultaneously develop efficient upstream and downstream technologies. PRODIAS is working on these aspects and Xendo is happy to contribute to this with our XPure Systems.

Ketogluconic, lactic, citric, succinic and many other organic acids are products that rely on a platform manufacturing technology. This means that most modern manufacturing facilities apply – to a large degree – the same processes. In both cases, the key step in the production process involves a fermentation followed by purification of products using at least one ion exchange step.

Application of a continuous countercurrent ion exchange technology for purification of these products result in significant advantages. In this memorandum, the effect of continuous ion exchange technology on purification of ascorbic acid will be elucidated.

L-Lysine is one of the essential amino acids, which cannot be synthesized in the body. The main application of Lysine is animal feed. The global market for food-grade L-Lysine is estimated at over 800,000 ton (2007 figure). The market price for bulk Lysine has dropped significantly over the past decade(s), forcing suppliers to apply more efficient manufacturing technologies.

This paper gives an overview of industrial SMB chromatography and focusses on the strategy how to develop a purification system either in the early development phase of a product or to assess whether a batch process can be optimised and scaled into a continuous process.

Biotechnological fermentation processes are widely used in industry to produce an abundant range of organic products which often need to be purified in order to meet high-quality standards.Typical bioprocesses comprise:

upstream (USP, e.g. prior to, and including fermentation

downstream (DSP following the fermentation-harvesting, e.g. purification and crystallisation)

Industrial Bioprocesses can be characterised by a few common rules of thumb:

Downstream processing: the basics

Conventional downstream processing involves biomass separation from the soluble fractions of the fermentation broth as a first step (e.g. filtration, centrifugation). Hereafter, other downstream process steps follow, depending on the required product purity and concentration. Decolorization is often necessary to remove the brownish colour of a fermentation broth, caused by degenerated sugar and proteins. Adsorption chromatography is widely used to bind the product of interest or the impurities to a specific resin (sorbens), packed in a column (packed bed). The bound product is then eluted and can be used in further processing like crystallisation. After elution, the resin/column is regenerated and cleaned (CIP-Cleaning In Place).

A typical process flow diagram is shown in the figure below.

Conventional bioprocesses can be summarised by the following steps:

Biomass removal (e.g. flocculation, filtration, centrifugation)

Decolorization

Adsorption Chromatography

Concentration and Crystallisation

Simulated Moving Bed Chromatography

In adsorption processes, the adsorbent is held in a (pressure) vessel, most often called a resin vessel. The stationary phase is referred to as a packed resin bed. As the process fluid flows through the vessel, the resin attains an equilibrium with the process fluid, resulting in a mass transfer zone that gradually moves through the bed. If the mass transfer zone has reached the exit of the resin bed, the bed is saturated and “breaks through”. The resin needs to be washed and regenerated before it can be loaded again. As a consequence, continuous processing of the liquid requires at least two fixed beds, but usually, three beds are installed.

In the previous century, the advantages of continuous countercurrent processing have been recognised for adsorption processes, as well as for other mass transfer processes.In SMB technology, the chromatography material is kept inside columns or vessels. The transport of the chromatography material is obtained by periodically switching in- and outlet positions.In the 1980’s, the SMB concept was originally developed for binary fractionation processes, where a stronger and weaker binding component are present in the feed solution and are separated into two product streams:

Extract phase, which contains the stronger binding component.

Raffinate phase, which contains the weaker binding component.

A state of the art example of such fractionating system is the production of High Fructose syrup fractions in the sugar industry. Here the Fructose is the monosaccharide with a stronger affinity towards the resin compared to Glucose.

At a somewhat later stage, the same concept has also been developed for bind and elute systems. Bind and elute systems typically comprise –at least- the following zones:

Adsorption of the active ingredient or, in some case, impurities

Adsorption wash, to replace the mother liquor (from fermentation broth) by water. This is to prevent contamination between elution and adsorption zone

Elution, to desorb the active ingredient that has been adsorbed in zone I

This zone distribution is not restricted to the four as mentioned, for instance, regeneration and cleaning in place have been frequently applied.Bind and elute SMB systems are designed in carrousel configuration, featuring a central rotating fluid distribution valve, and a static vessel configuration featuring a valve block for each individual resin vessel. Each valve block is identical and comprises a number of valves accommodating all in- and outlet flows that have been defined for the chromatographic cycle.

The below figure represents a typical conceptual flow diagram for a bind and elute system.

Bind and elute IX chromatography systems based on the SMB principle has opened a huge field of applications where valuable products are recovered or purified on a continuous basis thereby saving substantial water consumption as well as elute and regenerant agent.Xendo has the experience and capability to design and build custom-made SMB continuous Ion Exchange and Chromatography systems under the product name XPure™.

Development studies

In general, a process development study can be approached from different angles and started or initialised in different stages of the study.When developing a production process first the target objectives should be defined; what is the required yield and purity of the target compound; what is the composition of the starting material (feed); which recovery or purification process is most beneficial in terms of energy (including clean water) and material consumption and gives the least waste production; what is the scale of continuous operation.If industrial (IX) chromatography could be a (or one of) potential route, we then start surveying the literature on the presence of similar or equivalent applications for the particular compound or molecule under study.If literature cannot elucidate the case, based on the molecular structural or other adsorption relevant characterisation, a resin screening study can be conducted. The outcome would be one or several resin functionalities that are preferably commercially available.A lab scale column test on a representative feed sample – a so-called pulse-response test- repeated for a few different resin species will obtain a strong indication of the effectiveness of a specific adsorption system.Depending on the specific adsorption capacity of the target molecule onto the resin, further column tests – so-called breakthrough tests- will produce data on the resin capacity and information on how to elute (buffer composition, treatment ratio) the target molecule.

In the case, that potential resin candidates can be identified for the purification job the column tests can be elaborated with further break-through or pulse-tests at variable process conditions that cover the window of operation in a full-scale industrial setting. Typically this is conducted on one or two best performing resin candidates from the previous stage.Here a Design of Experiment approach combined with the rationale of experienced chromatography engineering practice is used to define how many column tests will be conducted and what parameters will be varied at different levels.

Based on the data from the extended tests a preliminary process design and CAPEX/OPEX estimate can be made. Here we have developed our design tool where all relevant parameters can be put in and the outcome shows a full-scale SMB configuration and equipment dimensions. Dimensional data refer to a number of individual resin cells, dimensions of resin cells, line and valve sizing and pressure drop per distinct zone.

The design tool is based on the 2-film mass transfer kinetics model which is the principle for which we have created an algorithm. The design tool further features the (universal) Kremser equation for counter-current contacting.A set of physical and mass flow-related variables have been accounted for. The most important parameters are:Resin porosity, particle size (specific area) and evidently the most important -- specific adsorption capacity; diffusivity in both liquid and stationary phase; void fraction of resin bed; bed velocity; fluid viscosity and temperature.

The design tool could also be deployed if the adsorption system is a state of the art process, or close to this. In that case lab scale column tests could be skipped, and the specific feed characteristics need to be combined with the (specific) resin type that could do the purification/recovery job.

The output of the design tool can be used to do preliminary cost and value engineering. The outcome is essential to evaluate the purification/recovery process.In the case of a positive decision, i.e. a (IX) chromatography process is the most beneficial and cost-effective route, the process can be optimised on a (slightly) larger scale.Here we can enter two different scales for piloting.A mini pilot or lab-SMB system featuring small resin cells up to 1-inch column diameter and on average 200-500 mm bed height that still can be operated on a lab scale.

1. A mini pilot or lab-SMB system featuring small resin cells up to 1-inch column diameter and on average 200-500 mm bed height that still can be operated on a lab scale.

2. A large pilot SMB system featuring a bit larger resin cells from 1-4 inch column diameter on average 400-1000 mm bed height.

The selection merely depends on the availability of adequate feed and buffer volumes, any uncertainties that may not adequately be identified on an industrial scale, for example, impurities presence and identification, the presence of suspended solids or temperature variations.The large scale pilot system typically works on site, close to the operating plant or at a pilot facility.

The outcome of a pilot study will be a robust design of the industrial scale process also featuring chemical consumption figures, product yield and purity. From the design data, the basic engineering of auxiliary equipment –like pumps, inter-stage tanks, piping, instrumentation etc.- can commence. Ideally, a commercial design proposal is the final delivery of a pilot study. The client/end user can now make a final assessment of the chromatographic process, possibly comparing this –if any- with alternative purification processes (e.g. batch wise adsorption, crystallisation, evaporation, distillation et cetera)

Considerations

Simulated Moving Bed has distinct benefits over classical single column systems with significantly higher yields / productivity and lower consumption of chemicals, water, and energy. Also, it lowers production cost due to the lowered column volume and diminished use of chromatographic separation medium (resin) and, of course, less labour.

This continuous production system is increasingly used on industry scale and also becoming more popular in the pharmaceutical, fine chemicals and food sectors due to its capability to be integrated into production plants, where it contributes by delivering high concentrations of product under the beneficial circumstances mentioned before. Because of these advantages, we see a bright future for this technology for separation, purification and recovery, turning simplistic batch separation operations into profitable continuous processes. Next to these advantages, SMB fits seamlessly into the developing trend of sustainable solutions and the realisation of a bio based economy.

If you’d like to investigate what SMB could mean for your production processes don’t hesitate to contact us or have a look at our currently available systems:XPure-C&XPure-S. We also have a wide variety of pilot studies available for those interested.

The static SMB system XPure-S that represents the by XPure patented valve system with a zero dead leg concept.The carrousel SMB system XPure-C featuring a turn table that carries the sorption containers going through the distinct process steps of a typical IXchromatography cycle.

The XPure-S SMB system offers a system for ion exchange processes with virtually unlimited scalability. The columns are not mounted on a carrousel and the valve manifolds can be designed to allow very large hydraulic throughputs. This makes the system suitable for any scale of operation.

In addition to this, the modular design of the fluid distribution system allows extension in a later stage without significant extra investments, by connecting additional valve manifolds and extra columns (and resin volume). This allows a stage-wise capacity extension of the plant without having to build an entirely new system.